Engine controls for internal combustion engines normally use physical models which have parameters by means of which the ideal state of the internal combustion engine can be described. In reality, the underlying parameters of the physical model generally deviate from the real parameters of the engine. In order to match the physical models to the actual conditions in the internal combustion engine, adaptations of the parameters are carried out which are based on a comparison between measured parameters and theoretically expected values. The parameters are adapted by applying one or more adaptation values to said parameters.
It is desirable for the adaptations to be executed such that adaptation values are applied to those parameters of the physical models which are actually the cause of the deviation between the physical models and the real conditions in the internal combustion engine. If those parameters which are actually the cause of the deviation between model and reality are adjusted with the aid of adaptation values, the physical models deliver precise results even when there are rapid changes in the working point of the internal combustion engine without a repeat adaptation being required. If other parameters are adapted which are not the cause of the deviation between model and the real conditions, then a repeat adaptation is generally required when there is a change in the working point. The assignment of deviations to the correct system parameters (parameters) can, however, be difficult since the number of sensors for measuring the parameters is frequently limited.
Such a problem is present in internal combustion engines which have an intake manifold pressure sensor in an intake pipe but do not have an air mass sensor, particularly in internal combustion engines with variable valve control. The intake manifold pressure in such systems depends above all on the flow cross-section at a throttle valve and on the absorption capacity of the engine. The absorption capacity of the engine is essentially determined by the settings of the intake and outlet valves and/or by the rotational speed of the internal combustion engine. If the intake manifold pressure sensor identifies an intake manifold pressure which is higher than the theoretically expected value, then this may be caused by a greater flow cross-section at the throttle valve then specified by the corresponding parameter or by a lower absorption capacity than specified by the corresponding parameter. If in this state the flow cross-section of the throttle valve is adapted upwardly, then the calculated air mass becomes too great and the injection quantity is mistakenly raised. This results in too rich an air/fuel ratio in the combustion chamber of the internal combustion engine. The air/fuel ratio that is too rich can be detected by means of the lambda probe. The measured air/fuel ratio leads to an adaptation of the quantity of fuel injected, which is reduced as result, i.e. the corresponding adaptation value for the fuel quantity is decreased. The desired air/fuel ratio can in this way be maintained. Although the model for a specified working point of the internal combustion engine can in this way be brought into harmony with the measurement values, nonetheless incorrect parameters are adapted which determine at another working point defective model parameters so that an adaptation has to be carried out afresh. Under changing operating conditions, this would result in the underlying physical model having to be adapted constantly to the changed operating state. As a result, an adaptation of the physical model can be implemented only when the operating state is static.
Such a physical model for determining the air mass flow, which is determined with the aid of the measured intake manifold pressure, is known from publication WO 97/35106. Furthermore, an adaptation is provided for permanently adjusting the model parameters in a stationary and in a nonstationary operation in order to adapt the accuracy of the selected physical model.